Panelboards are customarily designed to accept either bolt-in or plug-in circuit breakers, but not both types. Panelboards for bolt-in circuit breakers require frontal access for a tool used in making the line side connection, and therefore, are generally wider than their plug-in counterparts. From a manufacturing and distributing standpoint, it is desirable to standardize on such assemblies to the greatest extent possible to reduce the number of different parts, costs and inventories. It is also desirable to be able to interchange one type of breaker for the other in the field.
Some panelboards are designed to accommodate field interchangeability by changing the branch circuit connector of the panelboard. Only one panelboard design is known which accepts both types of breakers without modification, that being shown in the U.S. Pat. No. 3,356,906 to Raymond Lamb et al. dated Dec. 5, 1967. In that design, branch circuit connectors are formed to extend edgewise across the panelboard while the end thereof which attaches to the bus bar is formed over at right angles to the plane of the connector. The free end of the connector is unsupported and has a tendency to deflect and/or twist under the force required to connect a plug-in circuit breaker thereto. Another disadvantage of the above mentioned design is that the accommodation for the bolt-in connection is a raised central portion which occupies a substantial portion of the passageway between the rows of breakers. That passageway has a significant cooling effect on the panelboard in operation, and it is desirable to reduce the obstructions of that passageway to provide maximum cooling.